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Design question reflex/4th order bandpass

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DJ-Versatile View Drop Down
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    Posted: 25 April 2016 at 12:37pm
Hey Guys,
I'm designing my next lightweight portable system and I had a question. Excuse me if this sounds stupid.

If I lay this sub so the driver is pointing at the floor,  does it effectively change the cab into a 4th order bandpass box? It is not my plan to do so, but I was just being curious as to what the effects would be.

So from this



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Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 25 April 2016 at 2:35pm
Many domestic hi-fi subs squirt driver at floor, or for bandpass 6 designs, the ports squirt to the floor. Helps with Wife Acceptance factor, nice piano black lacquered box, with nothing to see. may stop small fingers from fecking too.

There was some fashion a while back for forming a V baffle from stacking two traditional reflex boxes, and putting a piece of wood over, to form a primitive horn, and to form a front V. What it achieved is really anybodies guess. Apart from cancellations around 800Hz and up, and dips from "horn throat" reflections being out of phase with direct radiated.

Depending on the height of the feet on the baffle, you would create a 4 sided "Port", but I do not know the maths of how you would work out the tuning frequency. You would have surface area of port equal to 4 x feet height x length of side (assume cubic box, so all sides are same length). Length of port would be equal to distance from centre of driver to side, perpendicularly? Trouble is, that describes a notionally triangular prism shaped port to each side, so god only knows how to model that, x4.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 25 April 2016 at 3:36pm
If the cabinet is directly on the floor, so the area in front of the driver is air tightly sealed by the floor , the cabinet becomes a 4th order BP. However it's common to have the closed chamber account for the lower tuning of the cabinet, while the ported chamber affects the high frequency roll off. So it would be a 4th order BP but not one with a common tuning.

If it's hovering close but an X amount above the floor, it becomes a 6th order. The best strategy imho would be to measure the impedance graph up to about 500- 1000 Hz and then find a model that agrees with the measured result. It could either be represented as a chamber with ports or a cavity resonance.

Down firing also helps with integration into the rest of the system, as higher order distortion created by the loudspeaker, after processing, will now only reach the ear indirectly.
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